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Originally Posted by SCOBRAC
The PI intakes were repaced by the sidewinder intakes which were replaced by the CJ intakes. The RPM performer and the CJ intakes are both more medium rise in nature and port size.
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I'm not sure of the order of the intakes, as I believe the sidewinder has an earlier casting date, although I haven't varified that. The sidewinder was the single 4 medium riser intake, the PI & CJ were for low riser engines. I checked my yellow Ford Performance book for port sizes, and according to that you're correct, the PI & CJ intakes have medium riser sized ports. I never realized that before. Strange that the CJ head ports are so much larger, although I guess that's not really abnormal. As a side note, the Ford Performance book lists medium riser heads as having 2.34" tall ports, the same as the CJs, and I know that's not true. I'm going to have to find another source to back up what this book states.
NKOTB, using the formula .257 x number of cylinders x cfm at max cam lift, 280 cfm will give you around 575 hp, although I don't think you'll be able to achieve 280 cfm without going to larger valves. I believe 2.150 intakes and 1.75 exhausts will fit in your combustion chamber, although the valves will be shrouded without having some clearance cut around the valves, giving you a bit larger combustion chamber and lowering your compression with your current pistons. This could be remedied by a smaller dish in the piston to bring the compression back up. My memory is fading on this, but I believe you can make the above valves by using .100 longer than stock BB Chevy intake valves, cutting the head size down and putting a back cut on the valves to narrow the valve margin. The back cut will also improve flow. Varify the lengths of the stock Ford valve and BB chevy intake + .100 before buying the valves and doing this, as there may be a flaw in my memory bank.
Dan